Method for removing a cable core from a cable sheath

ABSTRACT

The invention relates to a method for removing a cable core from a cable sheath, which cable core comprises an envelope ( 8 ), wherein, at an end of the cable ( 1 ), a flowable medium ( 22 ) is introduced under pressure into the cable tube ( 9 ) so as to reduce friction, and a tensile force (F) is exerted on the cable core at an end ( 5 ) of the cable ( 1 ). To provide a method by which existing cables can be freed from their core in as quick and inexpensive a manner as possible, it is provided for the flowable medium to be introduced precisely targeted into the annular space between the inner side of the cable sheath and the envelope ( 8 ) of the cable core.

[0001] The invention relates to a method for removing a cable core froma cable sheath of a cable, which cable core comprises an envelope,wherein at one end of the cable—the so-called proximal cable end—aflowable medium is introduced under pressure into the cable tube so asto reduce friction, and a tensile force is applied to the cable core atan end of the cable.

[0002] The present invention particularly relates to underground cablesfor telecommunication purposes, which usually comprise a cable core witha plurality of leads and at least on envelope surrounding themaltogether and provided e.g. by a paper winding. Moreover, such cablesmostly have a rigid cable sheath which may often be formed by a layer oflead (Pb) over which a steel layer and, in addition, a fabric orsynthetic material envelope may be arranged. Yet, the invention alsorelates to aerially supported cables, e.g. telecommunication cablesguided on high voltage towers.

[0003] The term flowable medium includes gaseous, liquid or pasty mediaor mixed forms thereof.

[0004] The rapid technical development in the field oftelecommunications requires the use of new data transmission lines viawhich higher data rates can be transmitted. In this connection,particularly optical waveguides with low attenuation are used, via whicha very high band width can be transmitted with little loss. At present,in particular following the liberalisation of telecommunication, thereexist efforts to replace the old cable networks by new networks ofhigher capacity.

[0005] The laying of new cables in the ground by means of costlyearthwork is also very expensive and time-consuming. With the prevailingcompetition in the field of telecommunications, this is not tolerable.

[0006] One method of renewing old cables consists in that tubes arefastened to the cables laid in the ground or the like, which tubes arepulled in when the existing cables are pulled out and thus take theirplace. Subsequently, optical waveguides, e.g., are laid in the tubes.What is disadvantageous is that the surrounding soil poses an enormousresistance to the cable or tube, respectively, to be inserted, so thatalways only short distances can be renewed without earthwork.

[0007] One method of removing inner conductors from cables is known e.g.from WO 82/00388 A1. In this known method, a fluid is introduced underpressure in the cable in coaxial mode of construction so as to break andremove the insulating material between the inner conductor and theshield. Subsequently, the inner conductor can easily be pulled out ofthe cable. In telecommunication cables comprising a plurality of innerconductors, the insulation is disintegrated by using appropriatesubstances, whereby the extraction of the inner conductors isfacilitated. Moreover, also the use of milling cutters or cutting toolsis provided for, which disintegrate the inner conductors of the cableand remove them appropriately. This known technique is very costly andtime-consuming and not generally useful for telecommunication cables.

[0008] A method of the present type is known from U.S. Pat. No.4,197,628 A, wherein the ends of a piece of cable are exposed and asleeve is fastened around one end of the cable. The sleeve is tightlysealed by a cap, and a lubricant is introduced under pressure into thecable core via a connecting piece on the cap. At the opposite end of thecable, the emergence of the lubricant is waited for, and subsequentlyfurther introduction of lubricant is stopped. After an envelope usuallyprovided externally on the cable core has been soaked with lubricant,the cable core is pulled out. In practice, this method has notprevailed, since here apparently only relatively short cable sectionscan be pulled out.

[0009] Therefore, the present invention has as its object to provide amethod of the initially defined type, by which existing cables can befreed from their cable cores as quickly and cost-effectively as possibleso as to be able to use the cable sheath then present as a tube for thelaying of, e.g., new data transmission cables, such as optic waveguidesor the like, and, on the other hand, be able to re-use the raw materialsof the cable core, in particular copper. The removal of the cable coreshall be possible over as long cable lengths as possible.

[0010] The object of the invention is achieved in that the flowablemedium is introduced precisely targeted into an annular space betweenthe inner side of the cable sheath and the envelope of the cable core.

[0011] Preferably, at least during part of the step of introducing theflowable medium, the annular space or the entire cable is notpressure-sealed at the other cable end (the so-called distal cable end)so that liquid medium under the action of pressure flows substantiallyin the annular space to the distal cable end. This partial steptherefore will also be termed “flow step” in the following.

[0012] Preferably, at least during part of the step of introducing theflowable medium, the annular space or the entire cable ispressure-sealed at the distal end so that the liquid medium under theaction of pressure compresses the cable core and/or expands the cablesheath. This partial step therefore will also be termed “compressionstep” in the following, wherein it must be noted that also during theflow step an (i.a. even higher) compression will occur.

[0013] Particularly preferably, in the scope of the present method, bothmentioned partial steps are carried out, i.e. at first the flow step andsubsequently the compression step. Advantageously, the flow step will beterminated and the compression step will be started when the flowablemedium emerges at the distal cable end.

[0014] The flow step primarily serves to transport the flowable mediumthrough the entire cable. A closer look shows that here the flowablemedium mainly moves in longitudinally extending depressions of the cablecore, which are derived from the leads structure of the cable core. Awetting of the interface between envelope and inner side of the cablesheath need not necessarily occur over the entire periphery, but only insmaller partial regions of the periphery corresponding to theaforementioned depressions. In the subsequent compression step, however,the higher lubricant pressure which builds up causes a (continuing)compression of the cable core (and, in cables with an elastic sheath,possibly also an expansion of the sheath), whereby the annular spacewill be widened over the entire periphery and by this, the entireinterface over the entire periphery will be wetted by lubricant.

[0015] In embodiments of the method in which the envelope of the cablecore to be pulled out is designed as a winding, it has proven to beparticularly advantageous to use that cable end as the proximal cableend towards which the winding proceeds. In other words, in this instancethe flowable medium is to be moved forwards in the annular space incounter-direction to the winding direction. The precisely targetedintroduction of the flowable medium into the annular space between theinner side of the cable sheath and the envelope will be assisted by thefact that the flowable medium is introduced against a possibly presentwinding direction of the envelope of the leads. Often the envelope ofthe leads of a cable consists of a strip, in particular of paper, whichis wound around the leads in overlapping fashion. By introducing theflowable medium in counter-direction to the winding direction of thisenvelope, a penetration of the flowable medium into the interior of thecable core is effectively prevented. The method is facilitated by thefact that the flowable medium is introduced at the same end of the cableas that end of the cable at which the cable core is pulled out (i.e., atthe proximal end). Thereby, most of the installations required for themethod need only be provided at one end of the cable. At the oppositeend of the cable (i.e. at the distal end), only the core sealing as wellas a closure of the cable end are effected. If, however, a woundenvelope of the core, e.g. in case of a helically arranged paperenvelope, is present, the extraction of the core in the windingdirection will be assisted, since the overlapped portions of the woundenvelope are not opened in fan-like manner. When pulling out the core inthe winding direction of the envelope, tearing open of the envelope willbe prevented and the extraction procedure will not be rendered moredifficult. Alternatively, however, the flowable medium may also beintroduced at the end of the cable other than that end of the cable atwhich the core is pulled out.

[0016] Besides, in such wound cable core envelopes, it has provenparticularly advantageous to pull out the cable core at that cable end,towards which the winding proceeds, i.e. to allow the pulling movementto be effected in the winding direction. In other words, it isparticularly advantageous to use that cable end as the proximal end,towards which the winding proceeds, and not only to effect theintroduction of the flowable medium, but also the extraction of thecable at this proximal end.

[0017] In a preferred embodiment, at least during part of the step ofintroducing the flowable medium, a compressed gas, in particularcompressed air, is introduced into the interior of the cable coresurrounded by the envelope. In this manner, a force acting from theinside towards the outside onto the envelope is effected, whereby theentry of the flowable medium into the cable core can effectively beprevented. In this manner, a counter-pressure acting on the envelopefrom within is produced against the flowable medium that is introducedunder pressure, improving the sealing of the envelope towards its innerside. Basically, this measure can be effected during the flow stepand/or the compression step or parts thereof. Preferably, however, thismeasure will be taken only during the compression step so as not toimpede the spreading of the flowable medium in the longitudinaldirection of the cable during the flow step, on the one hand and toassist in a high pressure build-up during the compression step, on theother hand. The pressure of the pressure gas is, i.a., markedly lowerthan that with which the flowable medium is introduced so as not toexcessively impede both, the flow of the latter in the longitudinaldirection of the cable and the compression of the cable core.

[0018] In the aforementioned embodiments which have an envelope designedas a winding, e.g. a helically arranged paper envelope, it is, moreover,advantageous to allow the compressed gas, preferably the compressed air,to flow in the interior of the cable core in the winding direction ofthe envelope. This favorably assists in a sealing of the overlappedportions of the winding and prevents tearing up of the overlappedportions of the envelope by the compressed air, which might result in amore difficult extraction of the cable core from the cable tube.

[0019] It is advantageous to admix a liquid medium, in particular anadhesive, to the compressed gas, in particular to the compressed air,which thereby is introduced into the interior of the cable core.Depending on the construction of the cable, the admixture of a liquidmedium to the compressed gas, or compressed air, respectively, may leadto a kind of gluing together of the overlapped portions of the envelope,so that penetration of the flowable medium into the cable core will bemade even more difficult. To humidify the compressed gas, water, oil orcertain adhesives may be used which are admixed to the pressurized gasto a slight degree. Such additions shall not build up a hydraulicpressure, by which the annular space would be reduced, but a mutualgluing together of the overlapping portions of the winding shall beattained. The volume defined by the cable core shall still remaincompressable so that a reduction of the volume will remain feasible bythe introduced flowable medium and, consequently, an enlargement of theannular space between the envelope and the inner side of the cablesheath can be attained. As the glue, component glues with retardedhardening which should be as low-viscous as possible, can be employed.

[0020] The precisely targeted introduction of the flowable medium intothe annular space may advantageously be effected in that the interior ofthe cable core at the proximal cable end is closed pressure-sealedrelative to the flowable medium to be introduced under pressure into theannular space, so that flowable medium cannot penetrate into theinterior of the cable core at the proximal cable end. The flowablemedium can then be pressed in at the end side of the cable; pressing inis, however, also possible through rearwardly offset radial bores in thecable sheath.

[0021] If the distal cable end were simply to be closed without avoidinga communication between the open end of the annular space and the openend of the interior of the cable core, flowable medium emerging from theannular space could enter into the interior of the cable core and flowback therein to the proximal end. To prevent this, preferably theinterior of the cable core also at the distal cable end is closedpressure-sealed relative to the annular space so that flowable mediumemerging from the annular space cannot enter there into the interior ofthe cable core.

[0022] In both instances, the pressure-sealed closure of the interior ofthe cable core relative to the annular space can advantageously beachieved by sealing attachment of a core seal to the respective end ofthe cable core. The core sealing is preferably effected by an elasticenvelope which is applied over the exposed leads. In doing so, avulcanisation band may, e.g., be used which causes an automatic gluingafter its application and thus an impervious envelope of the leads.

[0023] If it shall be possible to introduce compressed air or to ventthe interior of the cable core at the respective end, the core sealingpreferably is equipped with a venting tube.

[0024] By the fact that the cable core, at least at the proximal cableend, is enveloped, flowable medium cannot enter into the interior of thecable core at the front side thereof. In contrast, the flowable mediumis introduced precisely targeted into the annular space between theinner side of the cable sheath and the envelope, whereby a force actsfrom the outside on the cable core, which force will lead to thecompression of the cable core, whereby the annular space is enlarged, acomplete wetting of the annular space is assisted and the frictionduring the extraction is reduced. Thereby, greater lengths of old cablecan be freed from the cable core present therein in one procedure. Thelengths obtainable will depend i.a. on the type and diameter of thecable, the number of leads in the core, the pressure with which theflowable medium is introduced, the flowable medium used as well as thecourse of the curves of the cable. By removing the core from the cables,the material thereof, mostly copper, can be re-used, or the empty cabletube formed thereby may be used for laying new wires, e.g. In addition,environmental risks posed by the old cable are reduced.

[0025] The flowable medium preferably is introduced into the cable tubebefore the cable core is pulled out.

[0026] In addition, the flowable medium may also be introduced into thecable while the cable core is being pulled out.

[0027] If the cable core is equipped at both ends of the cable with acore sealing before the flowable medium is introduced, an entry of theflowable medium can also be prevented at the distal cable end.

[0028] To check the tightness and the permeability of the cable,compressed air can be introduced into the interior of the cable corebefore the flowable medium is introduced. To check the tightness, thepressure on the side of introduction of the compressed air is measuredwhile the compressed air is being introduced. From the measured pressurevalues, a pressure loss which is caused by a leaking site of the cablecan be determined. In such an instance, the cable can be cut apart infront of the leaking site, and the procedure for removing the core fromthe cable can be carried out for the new cable piece.

[0029] To check the permeability of the cable, the pressure is measuredon the side other than that of the introduction of the compressed air,while the compressed air is being introduced. In this manner, possiblesqueezed locations of the cable can be found. If, due to a verypronounced squeezing, for once an extraction were no longer possible,the cable can be cut off in front of this squeezed location and then themethod for removing the core can be carried out for the new cable piece.

[0030] During the introduction of the flowable medium, the distal endpreferably is open so that the air displaced by the flowable medium canescape.

[0031] While the flowable medium is being introduced, the cable corepreferably is tensioned so as to prevent an axial displacement of thelatter during the introduction of the flowable medium. This bias may,e.g., be effected via a tube which serves to introduce the compressedair into the cable core, the tube being glued together with the leads ofthe cable core and a tensile force of a certain extent being exerted onthe tube.

[0032] Introduction of the flowable medium is preferably interrupted ifthe latter emerges at the other end of the cable. In this manner, theamount of the flowable medium is limited to the volume required.

[0033] According to a further embodiment, it is provided that after theintroduction of the flowable medium, the two ends of the cable areclosed in an air-tight and pressure-sealed manner, the cable is providedwith a venting tube and that furthermore a pressure is exerted on theflowable medium. By this method step, due to the compression alreadyoccurring in the flow step, air present in the interior of the cablecore is pressed out through the venting tube, whereby the diameter ofthe cable core is reduced and thus a wetting of the annular space and,thereby, an extraction of the core is substantially facilitated. In thecompression step, on the other hand, it is rather advantageous not topermit venting of the cable core and even to introduce compressed airinto the latter, since here the amount of the air volume to be displacedis relatively small.

[0034] To prevent the cable core from rotating during the extractionprocedure and thus, from possibly enlarging its diameter, the cable corepreferably is secured against rotation during the extraction procedure.This may be effected e.g. by cantilevering means on a commonly usedcollar, via which the cable core is pulled out of the cable tube, thecantilevering means preventing a rotation of the core.

[0035] Alternatively, during the extraction procedure, the corepreferably could also be rotated into a possibly existing helicaldirection of the leads present in the cable core, since by this thediameter of the core will be reduced and thus an effect blocking theextraction procedure will not occur.

[0036] To allow for a further use of the flowable medium following theextraction procedure, it is provided that at that end of the cable atwhich the cable core is being pulled out, the flowable medium isstripped off and collected. Stripping off is effected in a simplemanner, e.g. by an elastic ring which grazes on the envelope and thusstrips off the flowable medium, whereupon it flows into a collectingfunnel, e.g., and from there onwards into a container.

[0037] To be able to re-use a particularly large portion of the flowablemedium, it is provided that at the distal end of the cable, during theextraction procedure of the core, the flowable medium is entrained bythe cable. This may be effected e.g. by means of a piston-like elementconnected to the end of the core, which element transports the flowablemedium through the cable sheath to the proximal end of the cable, where,as mentioned above, it is collected by a collecting funnel, e.g., and isguided onwards into a container.

[0038] To prevent a damage of the cable sheath during the extractionprocedure, the cable sheath preferably is secured against rotation atthat end at which the cable core is pulled out. This securing againstrotation may, e.g. be effected by a collar with cantilevering meanspresent therein.

[0039] The procedure for removing the core from the sheath may beassisted in that during the extraction of the core, a pressure force isexerted on the distal end of the core. In this manner, the tensile forcecan be reduced to a slight extent, thus reducing the risk of the corebeing torn. Moreover, the length of the cable which can be reached,which can be freed from its core in one procedure, can be increased byassisting the extraction procedure.

[0040] The supporting pressure force may be applied via a flowablemedium introduced under pressure to the end of the cable other than thatfrom which the core is pulled out. In this instance, however, arelatively large amount of flowable medium is required.

[0041] According to a further embodiment, the tensile force istransmitted to the core via a clamp which is fastened to the core. Thisconstitutes a simple method for carrying out the method according to theinvention.

[0042] Just as well, the tensile force can be applied to the core via amotor-driven shaft around which the core is wound several times. In thisinstance, a sufficient length of the core is exposed and wound severaltimes about the motor-driven shaft, drum or the like, resulting in asufficient friction so that the rotating movement of the shaft, drum orthe like can be transmitted as a tensile force on the core.

[0043] To further facilitate extraction of the core, and to obtainlarger lengths of the core to be extracted, according to a furtherfeature of the method, the introduced gas and/or the introduced liquidmay contain an admixed lubricant, or the flowable medium itself may beformed by a lubricant. The lubricant may be provided in liquid or solidform. When using a gas introduced into the cable under pressure, theintroduction of a powderized lubricant has proven suitable.

[0044] If a thixotropic liquid is used as the lubricant, the undesiredentry of the flowable medium into the core can additionally be preventedor reduced, respectively. Thixotropic liquids have a viscosity that isdependent on the shearing stress, whereby depositing of the flowablemedium can be prevented. Thixotropic properties are to be found e.g. inpotassium soaps or oils with certain admixtures. Besides the thixotropicproperties, the lubricants or the liquid media, respectively, should beas inexpensive as possible and, ideally, also biologically degradable.

[0045] The changing of old cores for e.g., optical data transmissioncables can be further facilitated and accelerated if at least one newcable or the like is pulled into the cable tube while the core is beingpulled out.

[0046] The present invention will be explained by more detail by way ofembodiments and figures illustrating the same. Therein,

[0047]FIG. 1 shows the use of one embodiment of the method according tothe invention at an underground cable, seen in side view;

[0048]FIG. 2a shows the end of the cable according to detail II in FIG.1 during a first method step;

[0049]FIG. 2b shows the end of the cable during the introduction of theflowable medium;

[0050]FIG. 2c shows the end of the cable according to detail II of FIG.1 before the pulling out or extraction of the core is started;

[0051]FIG. 2d shows a side view onto the end of the cable according toFIG. 2c;

[0052]FIG. 3a shows the other end of the cable according to detail IIIof FIG. 1 at the point of time of the method shown in FIG. 2a;

[0053]FIG. 3b shows the end of the cable according to detail III of FIG.1 during the introduction of the flowable medium;

[0054]FIG. 3c shows the end of the cable according to detail III of FIG.1 before the core is pulled out;

[0055]FIG. 4 shows a perspective view of a clip for pulling out the corewith a means for protecting the core from being rotated;

[0056]FIG. 5 shows a longitudinal section through a cable with a woundconvoluted covering.

[0057]FIG. 1 shows a cable 1 as has been used, or is still being used,respectively, e.g. in telecommunication, which usually is laid in theground 2. To employ the method according to the invention, the cable 1is exposed and severed at a certain location, the so-called starting pit3. At a certain distance from the starting pit 3, e.g. 100 or 200 m, aso-called target pit 4 is made, and the cable 1 is also exposed andsevered. Thus, there results a piece of cable 1 of a certain length withan end 5 located in the starting pit 3 as well as with an end 6 locatedin the target pit 4.

[0058] By way of FIGS. 2a to 2 d, and 3 a to 3 c, respectively, whichshow details II and III, respectively, of FIG. 1 in enlargedillustrations during different method steps, an embodiment of the methodaccording to the invention will be explained in more detail in thefollowing. Usually the cable comprises a plurality of leads 7 made ofmassive copper or of copper strands and a leads insulation, e.g. made ofpaper or of a synthetic material. Moreover, groups of leads 7 may besurrounded by further insulations made of paper or synthetic material.Finally, the entirety of the leads 7 is surrounded by an envelope 8,preferably made of paper or synthetic material. The leads 7, theenvelope 8 and optionally additional, further inwardly locatedenvelopes, longitudinal fibers etc. together form the cable core. Toprotect the cable core from external mechanical and chemical influences,an inner sheath 9 is arranged which may consist of lead (Pb). Usually afurther sheath layer 10, mostly of steel, in particular of a helicallyapplied steel sheet, is arranged over the inner sheath 9, which sheathlayer 10 additionally protects the cable 1 from mechanical influences.Externally on the steel layer 10, a further insulation 11, e.g. ofoil-soaked fabric or synthetic material, may be provided which protectsthe steel sheath 10 from environmental influences. All together, thesheath layers 9 to 11 form the cable sheath. The cable core with itsenvelope 8 contacts the interior of the cable sheath substantially overits entire periphery, the cable sheath partially even encloses the cablecore with a certain tension. By the “annular space” between cable coreand cable sheath thus a space located between two interfaces (theoutside of the cable core and the inside of the cable sheath) is to beunderstood, wherein the radial extension of the annular space may be assmall as desired because of the direct contact of the interfaces. Theend of the cable 1 in the starting pit 3 constitutes the so-calledproximal cable end 5, the end of the cable 1 in the target pit 4, on theother hand, constitutes the so-called distal cable end 6. At the end ofthe method described in the following, a tensile force is applied to thecable core at the proximal cable end 5 in the starting pit 3 forextracting the cable core.

[0059] To start the method, the proximal cable end 5 from which the coreis to be pulled out, is peeled by removing the cable sheath, i.e. theinsulation 11, the steel sheath 10 as well as the lead (Pb) sheath 9,over a certain length, so that the cable core, i.e. the leads 7 and theenvelope 8 project from the cable 1 for a certain length. As thefollowing method step which is more clearly visible in FIG. 2a, anaerating and venting tube 12 is inserted into the cable core and therepreferably is glued together with the latter. Subsequently, the end ofthe cable core plus its envelope 8 is enveloped by a core seal 13, e.g.a self-vulcanising rubber band, resulting in a preferably airtight andpressure-sealed closure of the cable core at the proximal cable end 5. Avulcanisation band has the advantage that the latter will automaticallyglue to the envelope 8 and to the aerating and venting tube 12,respectively, whereby a tight closure can be realised. Subsequently, asleeve 14 made of metal, e.g., is pushed over the proximal cable end 5.The sleeve 14 may be provided with a bore 15 via which glue can bepressed in so that the annular space between the inner side of sleeve 14and the outer side of the cable sheath is filled with the glue and areliable connection of the sleeve 14 with the cable sheath is obtained.As glue, e.g. a two-component glue may be used which causes a rapid andreliable connection. The sleeve 14 serves to stabilize and secure thecable sheath to avoid damage by excessive axial forces when insertingthe flowable medium under pressure, and during the later extraction ofthe cable core from the cable sheath, respectively.

[0060] According to FIG. 3a, the distal cable end 6 in target pit 4 justas the proximal cable end 5 are cut off, peeled, provided with anaerating and venting tube 12 and, finally, the cable core is providedwith a core sealing 13. Finally, also a sleeve 14 is laid around thecable sheath and glued together with the latter.

[0061] In other (not illustrated) embodiments, no aerating and ventingtube is arranged at the proximal cable end 5. Yet also there the coresealing 13 closes the interior of the cable core pressure-sealed againstthe entry of flowable medium.

[0062] According to FIG. 2b, finally, at the proximal cable end 5 ofcable 1, a lid 17 is arranged over sleeve 14 and tightly connected withthe former. This connection preferably is effected via a thread 18 atthe outer side of sleeve 14 to which the lid 17 is screwed. Ifnecessary, additional sealing material may be used. The lid 17optionally has an opening 19 in the middle of its end side, throughwhich the aerating and venting tube 12 can be put. On the sheath of thecylindrical part of lid 17, a further opening 20 is provided via whichthe feed line 21 for the flowable medium or lubricant 22, respectively,is connected. As is schematically visible in FIG. 1, the feed line 21 isconnected to a pump 23 which in turn is connected to a container 24 forthe lubricant 22. In case of an envelope 8 helically wound around theleads 7, the flowable medium or lubricant 22, respectively, ispreferably introduced in counter-direction to the winding direction ofenvelope 8 (to define the winding direction: cf. FIG. 5), so that thereis a tendency for the overlapping portions of the winding to be closedby the flow direction of the lubricant 22, whereby an entry of theflowable medium or lubricant 22 from the annular space into the cablecore is reduced. In case of a wound envelope 8, the cable core,moreover, preferably is pulled out in the winding direction, because inthis way the overlapping portions of the envelope 8 will not be openedlike a fan during the extraction process and will not straddle againstthe extraction movement.

[0063] The flowable medium or lubricant 22, respectively, preferably hasa lower density than the volume enclosed by the envelope 8. As hasalready been mentioned, gaseous, liquid or pasty media or mixed formsthereof are used as the flowable medium. The aerating and venting tube12 is fixed with the lid 17 via appropriate union nuts 27, wherein atensile force can be exerted on the aerating and venting tube 12 priorto fixing so that the core will be pre-stressed. Instead of beingprovided in lid 17, the opening 20 in theory can also be provided insleeve 14 or in a corresponding extension of sleeve 14, and from therealso the lubricant 22 can be introduced. However, sleeve 14 is designedas an expendable part, and therefore also the structural meanspreferably are arranged on lid 17 which can be used several times. Whenthe cable core has been removed from cable 1, sleeve 14 may serve asconnecting piece for re-connecting the cable pieces, if cable 1 again isbeing used as a tube for an optical waveguide, e.g., or the like.

[0064] As can be seen from FIG. 3b for the distal cable end 6, alsothere a lid 17 is arranged over the cable end 6, and the aerating andventing tube 12 is fixed to the lid 17 by corresponding union nuts 24.Opening 20 on lid 17 and the aerating and venting tube 12 at first arekept clear. If compressed air is to be admitted to the interior of thecable core, the aerating and venting tube 12 may be connected via a duct25 to a compressor 26 for producing the compressed air (FIG. 1).

[0065] Before carrying out the method proper, compressed air can beblown into the interior of the cable core via the aerating and ventingtube 12, and the pressure can be monitored at the other end of the cablewith the help of a manometer 28. By this measurement, the cable 1 ischecked for it permeability. With the assistance of the pressure gaugeusually provided on the compressed air compressor or on a compressed airconnection 25, it can furthermore be checked whether or not cable 1 istight, since a possible site of a break could be located by aninsufficient pressure increase. When the cable has been checked for itstightness and permeability, finally, the end of the aerating and ventingtube 12 will be closed (not illustrated) at the proximal cable end 5,e.g. by means of a rotatable closing means which is screwed onto theaerating and venting tube 12.

[0066] Now the method as such will start, i.e. the so-called flow step.For this purpose, via feed line 21 lubricant 22 is introduced underpressure via opening 20, the annular gap at the distal cable end 6 beingopen. The lubricant 22 enters the annular space between the lead (Pb)sheath 9 and the envelope 8 precisely targeted and there flows in thelongitudinal direction of the cable to the distal cable end 6, withoutthe risk of the lubricant 22 penetrating into the cable core. Compressedair may already be admitted to the interior of the cable core during theflow step. Preferably, in case of a wound around envelope 7, thecompressed air will be introduced from the distal cable end 6, so thatthere will be a tendency of the flow of compressed air closing theoverlapped portions of the winding, instead of opening them in fan-likemanner. The pressure within the cable core presses the overlappedportions onto each other and thus makes it difficult for the lubricant22 to penetrate into the interior of the cable core. By adding a liquidmedium to the introduced compressed air, the overlapped portions of theenvelope 8 can be caused to glue together. The liquid medium may bewater, oil, or certain adhesives admixed to a particularly slight degreeto the compressed air. Finally, the lubricant 22 makes its way throughthe annular space between the lead (Pb) sheath 9 and the envelope 8 asfar as to the distal cable end 6. As soon as the lubricant 22 emergesfrom the opening 20 on lid 17 at the distal cable end 6, the annularspace at the distal cable end 6 is sealed, this being done by closingthe opening 20. Now the so-called compression step will start. Thecontinued pressing in of the lubricant now does not mainly serve totransport the lubricant 22 through the annular space along cable 1(naturally resulting already in a compression of the cable core), but itserves to build up pressure in the annular space, since the distal endof the annular space has now been closed. Whereas in the preceding flowstep the lubricant 22 preferably only has moved along in longitudinaldepressions of the envelope 8 (caused by the leads structure of thecable core) and therefore has not wetted the interface between envelope8 and the inner side of the cable sheath over its entire periphery,there is now a (continuing) compression of the cable core (and possibly,an expansion of the cable sheath, if the latter is not completelyrigid), whereby the lubricant 22 now will wet the said interface overits entire periphery. When a sufficient pressure has been built up, thepress-in procedure of the lubricant will be stopped. The pressureapplication on lubricant 22 will be terminated when the pressure remainssubstantially stable and a further compression of the cable core is nolonger possible. The lubricant 22 can be admixed to the flowable medium,or the flowable medium itself can be formed by the lubricant 22. Thepressure applied to the lubricant 22 will depend on the structure ofcable 1, the length of cable 1 as well as on various other factors.Finally, also flowable media are suitable, in which the lubricant iscombined with a solvent that evaporates after some time. Thisfacilitates the introduction of the liquid medium by dilution with thesolvent, and finally, after evaporation of the solvent, there results animproved sliding action on account of the more viscous lubricantremaining.

[0067] Finally, according to FIG. 2c, the lid 17 is screwed off theproximal cable end 5, and the aerating and venting tube 12 is removed.Subsequently, a stripping means 29 for the lubricant 22 is fastened overthe proximal cable end 5, which may be done e.g. by utilizing the thread18 on sleeve 14. The stripping means 29 may be substantially annularlydesigned and have an elastic edge grazing on the envelope 8 so that thelubricant 22 is stripped off the envelope 8 when the cable core ispulled out and will flow downwards on account of gravity, where it canbe collected by an appropriate funnel and an appropriate container (notillustrated) and re-used to a great extent. Finally, a clamp 30 istightly connected over the core sealing 13, and a tensile force in thedirection of arrow F is exerted on this clamp 30.

[0068] At the distal end 6 of cable 1, the lid 17 is also removed. Withthe core sealing 13 at the distal cable end 6, one or more piston-likeelements, e.g. discs 32 maintained in spaced relationship by spacerelements 31 can be arranged which entrain the lubricant 22 when thecable core is pulled out of cable 1 so that the lubricant emerges at theend 5 of cable 1 and is stripped off by the stripping means 29, where itcan be collected and re-used. During the extraction of the cable corefrom the cable sheath, it is suitable to secure the cable core againstrotation. This can be effected in various ways, e.g. by arms 33 orcantilevering means which are fastened to the clamp 30 and thus make arotation impossible. In addition, sliding skids 34 can be fastened tothe arms 33, which skids will slide on the ground while the core isbeing extracted (cf. FIG. 4). Furthermore, it is suitable also to securecable 1 against rotation, which can be realized by arms or cantileveringmeans arranged on the sleeve 14 in a similar manner as illustrated inFIG. 4. Simultaneously with the extraction of the cable core, a newcable, e.g. a modern optical waveguide or the like, can be connected tothe end of the cable core at the distal end 6 and thus can be pulledinto the cable sheath that now forms a tube, simultaneously with thepulling-out procedure.

[0069] To avoid a damage to the envelope 8 at the proximal cable end 5,the cable core preferably is pulled out of the cable sheath straightover a certain length, before an intentional change of direction ismade, e.g. so as to get the cable core from the starting pit 3 onto anappropriate reeling means (not illustrated).

[0070]FIG. 5 illustrates the definition of the “winding direction” ofthe envelope 8 by way of a longitudinal section. When a strip is woundaround the bundle of leads 7, there result scale-like overlaps inlongitudinal section, wherein always the first laid winding is partiallycovered by the subsequent winding. The winding direction extends alongthe cable 1 and is that direction in which the winding proceeds while itis being made. In FIG. 5, the winding direction is indicated by arrow W.The preferred direction for introducing the lubricant is incounter-direction to the direction of arrow W so that the overlappingportions of the strip-type envelope 8 will be closed by the flow of thelubricant. The preferred direction for introducing the compressed airinto the interior of the cable core surrounded by the envelope 8 is inthe winding direction, in the direction of arrow W, since by this theoverlaps of the strip-shaped envelope 8 will be rather closed thanopened. Finally, the preferred direction for pulling out the cable coreagain is in the direction of the arrow W of the winding, since by thisthe overlapping portions of the strip-shaped envelope 8 will be closedduring the extraction movement.

[0071] The Figures only show an exemplary embodiment of the invention.Structural changes and differences in the method course are possiblewithin the scope of the claims.

1. A method for removing a cable core from a cable sheath of a cable,which cable core comprises an envelope, wherein, at an end of thecable—the so-called proximal cable end—a flowable medium is introducedunder pressure into the cable tube so as to reduce friction, and atensile force is exerted on the cable core at an end of the cable,characterised in that the flowable medium is introduced preciselytargeted into an annular space between the inner side of the cablesheath and the envelope of the cable core.
 2. A method according toclaim 1, characterised in that at least during part of the step ofintroducing the flowable medium, the annular space or the entire cableis not pressure-sealed at the distal cable end, so that liquid mediumunder the action of pressure flows substantially in the annular space tothe distal cable end, whereby a so-called flow step is formed.
 3. Amethod according to claim 1 or 2, characterised in that at least duringpart of the step of introducing the flowable medium, the annular spaceor the entire cable is pressure-sealed at the distal end so that theliquid medium under the action of pressure compresses the cable coreand/or expands the cable sheath, whereby a so-called compression step isformed.
 4. A method according to claim 2 or 3, characterised in that atfirst the flow step and subsequently the compression step is carriedout.
 5. A method according to claim 4, characterised in that after theemergence of the flowable medium at the distal cable end, the flow stepis terminated and the compression step is started.
 6. A method accordingto any one of claims 1 to 5, characterised in that in a cable in whichthe envelope of the cable core is designed as a winding, that cable endis used as the proximal cable end towards which the winding proceeds, sothat the flowable medium is moved forwards in the annular space incounter-direction to the winding direction.
 7. A method according to anyone of claims 1 to 6, characterised in that in a cable in which theenvelope of the cable core is designed as a winding, the cable core ispulled out at that cable end towards which the winding proceeds, i.e.that the pulling movement is effected in the winding direction.
 8. Amethod according to any one of claims 1 to 7, characterised in that atleast during part of the step of the introduction of the flowablemedium, in particular during a compression step, a compressed gas, inparticular compressed air, is introduced into the interior of the cablecore surrounded by the envelope, whereby a counter-pressure acting onthe envelope from within is produced against the flowable medium that isintroduced under pressure.
 9. A method according to claim 8,characterised in that in a cable in which the envelope of the cable coreis designed as a winding, the compressed gas is introduced at that cableend from which the winding extends so that the compressed gas flows inthe interior of the cable core in the winding direction.
 10. A methodaccording to claim 8 or 9, characterised in that a liquid medium, inparticular an adhesive, is admixed to the compressed gas and thus isintroduced into the interior of the cable core.
 11. A method accordingto any one of claims 1 to 10, characterised in that the interior of thecable core at the proximal cable end is closed pressure-sealed relativeto the flowable medium to be introduced under pressure into the annularspace, so that flowable medium cannot penetrate into the interior of thecable core at the proximal cable end.
 12. A method according to any oneof claims 1 to 11, characterised in that the interior of the cable coreat the distal cable end is closed pressure-sealed relative to theannular space so that at the distal cable end flowable medium emergingfrom the annular space cannot enter into the interior of the cable core.13. A method according to claim 11 or 12, characterised in that thepressure-sealed closure of the interior of the cable core relative tothe annular space is achieved by sealing by attaching a core sealing tothe end of the cable core.
 14. A method according to claim 13,characterised in that the core sealing is equipped with a venting tubefor venting the interior of the cable core.
 15. A method according toany one of claims 1 to 14, characterised in that the flowable medium isintroduced into the cable tube before the core is pulled out.
 16. Amethod according to claim 15, characterised in that the flowable mediumis introduced into the cable while the cable core is being pulled out.17. A method according to any one of claims 1 to 16, characterised inthat the interior of the cable core at both ends of the cable is closedin a pressure-sealed manner relative to the annular space before theflowable medium is introduced.
 18. A method according to any one ofclaims 1 to 17, characterised in that the tightness of the cable ischecked with compressed air before the flowable medium is introduced.19. A method according to any one of claims 1 to 18, characterised inthat the permeability of the cable is checked with compressed air beforethe flowable medium is introduced.
 20. A method according to any one ofclaims 1 to 19, characterised in that the cable core is tensioned whilethe flowable medium is being introduced.
 21. A method according to anyone of claims 1 to 20, characterised in that the cable core is securedagainst rotation during the extraction procedure.
 22. A method accordingto any one of claims 1 to 21, characterised in that during theextraction procedure, the cable core preferably is rotated into apossibly existing helical direction of wires present in the cable core.23. A method according to any one of claims 1 to 22, characterised inthat at that end of the cable at which the cable core is being pulledout, the flowable medium is stripped off during the pull-out procedureand collected.
 24. A method according to any one of claims 1 to 23,characterised in that at the other end of the cable than that end atwhich the cable core is being pulled out, the flowable medium isentrained by the cable core during the extraction procedure, e.g. by apiston-like element connected to the end of the cable core.
 25. A methodaccording to any one of claims 1 to 24, characterised in that during theextraction procedure, the cable sheath is secured against rotation atthat end at which the cable core is pulled out.
 26. A method accordingto any one of claims 1 to 25, characterised in that during theextraction procedure, to assist the extraction of the cable core, apressure force is exerted on that end of the cable core which faces awayfrom the pulling side.
 27. A method according to claim 26, characterisedin that the pressure force is applied via a flowable pressing-out mediumintroduced under pressure to the end of the cable core that faces awayfrom the pull side.
 28. A method according to any one of claims 1 to 27,characterised in that the pulling force is transmitted to the cable corevia a clamp which is fastened to the cable core.
 29. A method accordingto any one of claims 1 to 28, characterised in that the pulling force isapplied to the cable core via a motor-driven shaft about which the cablecore is wound several times.
 30. A method according to any one of claims1 to 29, characterised in that the introduced, flowable medium containsan admixed lubricant.
 31. A method according to any one of claims 1 to30, characterised in that the flowable medium itself is formed by alubricant.
 32. A method according to claim 30 or 31, characterised inthat the lubricant is formed by a thixotropic liquid.
 33. A methodaccording to any one of claims 1 to 32, characterised in that at leastone new cable or the like is pulled into the cable sheath simultaneouslywith the extraction of the core.